Our invention is directed to a sizing apparatus for a prosthetic heart valve with an improved supra annular suture ring.
Mechanical artificial heart valves for humans are frequently fabricated from a form of carbon known commercially as Pyrolite.TM. carbon, a trademark of Carbomedics, Inc., the assignee of our present invention. Pyrolitic carbon is employed because of its unusual non-thrombogenic properties. Moreover, it is lightweight, hard and quite strong.
A standard implantable mechanical heart valve usually has an annular valve housing or body to provide a passageway for blood. Leaflets are mounted in the annular body and open or close the blood flow passageway. Usually there are one or two leaflets, but occasionally triple leaflet configurations have been proposed. On the outside of the valve body there is usually a circumferential groove. This groove is used to attach a suture ring to the valve body.
The suture ring is used to sew the heart valve to the patient's heart tissue. The ring generally comprises a knit fabric tube which is rolled into a toroidal form and which is secured about the heart valve body in the circumferential groove. Various methods and apparatus have been proposed for securing the suture ring to the heart valve. It is known, for instance, to bind the ring into the groove with a plastic thread. It has also been proposed to form a rotatable suture on the heart valve using heat shrinkable plastic material, as disclosed in U.S. Pat. No. 3,781,969. U.S. Pat. No. 3,491,376 suggests that a suture ring should be formed as a separate sub-assembly which should then be attached to the heart valve. In the '376 patent, the suture ring is described as including a resilient annular member which is temporarily deformed, so as to snap onto the valve body. U.S. Pat. No. 3,579,642 proposes the use of metal snap rings which must be radially expanded to place the suture ring about the valve body.
In U.S. Pat. No. 4,743,253, Magladry proposed a two-part suture ring comprising the knit fabric and an internal crescent-shaped ring which would be deformed inwardly by electromagnetic forming to clamp the heart valve while permitting relative rotation between the suture ring and the heart valve.
In U.S. Pat. No. 5,071,431, Campbell, et al. disclosed a suture ring comprised of essentially three parts: a stiffening ring which fits over an outer surface of a heart valve; a knit fabric sewing cuff attached to the stiffening ring, and a locking ring for securing the stiffening ring to the heart valve.
It has been found that the efficiency of a prosthetic heart valve is most dependent on the size of the valve. In other words, improved hemodynamic characteristics can be expected if the central orifice of the heart valve is made as large as possible with respect to the patient's anatomy. In the past, however, prosthetic heart valves have been implanted wholly or partially within the annulus of the excised natural valve. This strategy results in an effective reduction in the flow area by the combined amount of area taken up by the valve body wall, stiffening ring and suture ring.
To overcome this problem, a prosthetic heart valve can be used with a suture ring and stiffening ring combination which permits the prosthetic heart valve to be implanted above the site of the excised valve, for example, in the Sinus of Valsalva. Preferably, such a valve comprises an annular suture ring with a flared upstream edge having a smooth transition with an upstream edge of a heart valve. To use such a valve successfully, however, a sizer is needed.